The specificity of tumor therapy is often a limiting step in determining the success of a treatment. In fact, the onset of toxic effects and the reduced tolerability of certain anticancer agents limit their use and the quality of life of patients.
The reduction of toxicity is directly linked to the selectivity of the treatment for cancer cells. Monoclonal antibodies represent the ideal means for the specific targeting of tumors and, when combined with the avidin/biotin amplification system, constitute an extremely powerful and selective way to deliver active moieties at the tumor site.
Tenascin is one of the extracellular matrix proteins and shows site-restricted expression during embryogenesis and can be found in adult tissues during wound healing and tumorigenesis, as well as in newly formed tumor blood vessels. Tenascin is absent in normal adult tissue, but is expressed in the stroma of a variety of solid tumors, such as gliomas (Burdon, et al., Cancer Res. 43:2796-2805, 1983), mammary (Chiquet-Ehrismann, et al., 1986), lung carcinomas (Natali et al., Intl. J. Cancer 54:56-68, 1989), fibrosarcomas and squamous cell carcinomas (Rainos D. M. et al., Int. J. Cancer 75:680-687, 1998). Tenascin is found in gliomas, but not in normal brain tissue. For a discussion on tenascin, reference can be made to WO 92/04464, Wistar, and the related references.
Based on the teaching of EP 0 496 074, G. Paganelli et al developed a three-step pre-targeting approach for the systemic and locoregional treatment of tumors (Cremonesi M. et al., Eur. J. Nucl. Med. 26(2):110-120, 1999; Paganelli G. et al., Eur. J. Nucl. Med. 26(4):348-357, 1999; Paganelli G., et al., Cancer Biother. & Radiopharm. 16(3):227-235, 2001).
Other references on the three-step pre-targeting method are WO 94/04702 and U.S. Pat. No. 5,578,287.
The three step pre-targeting treatment is based on intravenous, sequential administration of a biotinylated anti-tenascin monoclonal antibody, streptavidin, and 90Y-labelled biotin with two chasing administrations of avidin and biotinylated albumin before streptavidin and 90Y-labelled biotin, respectively, to reduce non specific background. The selectivity of Paganelli's three step pre-targeting approach relies on the use of an anti-tenascin monoclonal antibody. Targeting of extra cellular matrix, compared to targeting of tumor cell antigens, exhibits the advantage of being unaffected by antigen modulation of tumor cells thus representing an ideal target for anti-tumor therapy.
The doses and timing of administrations of the three step pre-targeting treatment have been fixed in order to achieve optimal tumor/non tumor distribution ratio. Data obtained from 48 glioblastoma (GBM) or anaplastic astrocytoma (AA) patients, included in Paganelli's study, showed a substantial lack of toxicity, with the exception of some allergic reaction to streptavidin (which can be overcome by using avidin), and preliminary indication of therapeutic efficacy. In fact, 2 months after the end of treatment, 25% of patients showed a reduction in tumor size (Complete Response (Tumor reduction >50%)=6%; Partial Response (Tumor reduction <50%)=11%; Minor Response (Tumor reduction <25%)=8%) and 52% of patients had not progressed, with an overall response rate of over 77%. In some of these patients, whose life expectancy was less than six months, the response persisted for more than a year (Paganelli et al., 1999).
The role of biotinylated anti-tenascin antibody is to localize at the tumor site and display biotins to mediate subsequent avidin and 90-Y-biotin accumulation.
Anti-tenascin antibodies are disclosed, for example, in U.S. Pat. No. 5,624,659, Duke University, JP 2219590, Rikagaku and the above mentioned WO 92/04464.
An anti-tenascin antibody is disclosed in Siri A. et al., Nucl. Acid Res. 19(3):525-531, 1991; Balza E. et al., FEBS 332:39-43, 1993 and its use for therapeutic purposes is disclosed in the above mentioned Cremonesi M. et al., Eur. J. Nucl. Med. 26(2):110-120, 1999; Paganelli G. et al., Eur. J. Nucl. Med. 26(4):348-357, 1999;, Paganelli G. et al., Cancer Biother. & Radiopharm. 16(3):227-235, 2001. The clone used for generating the anti-tenascin antibody in the art is known as BC4.
The present applicant found the BC4 clone unsuitable for industrial development and regulatory purposes due to the production of an additional, non functional light chain (most likely of parental myeloma origin) whose level of expression increased under the pressure of scaling up cultivation, thus preventing large scale antibody purification.